Tidal power is a kind of hydropower that generates electric power by converting the energy of tides. Tidal power, although not a prime source of energy currently, has a great potential to be used for electricity generation in the future. Total availability of tidal power is restricted by its relatively high cost and limited number of sites having high flow velocities and tidal ranges. However, with the recent advancements in tidal technologies, the total availability of tidal power in terms of turbine technology as well as design may be higher than before, and the economic costs may be reduced significantly to competitive levels.
Generally, tide mills are widely used in Europe and along the Atlantic coast of North America. Recent reports state that the UK, which has the largest tidal and wave resource in Europe, is capable of harnessing up to 153GW of tidal power capacity with the help of three types of technologies and thus meeting 20% of current UK electricity demand and reducing carbon emissions. Hence it is evident that wave and tidal energy could contribute more to the increasing electricity demands across the globe.
How is Tidal Power Generated?
All the coastal regions experience two high tides and two low tides for a period of 24 hours. In such cases, the tidal difference between low and high tides has to be harnessed into electricity. The difference must be more than 16 ft for generating electricity from tides. However, only around 40 regions on Earth have tidal ranges of this magnitude.
Tidal power can be generated using the following technologies:
Barrages or Dams
Barrages are built across a bay or river estuary. Each of them consists of gates for allowing the water to flow into the barrage along with the incoming tide. These gates are then closed for preventing the tides from going out. The water trapped inside the barrage is known as a hydrostatic head. More power can be generated with the large amount of head. When the tides produce an adequate difference in the water level, the other gates on the opposite side of the barrage is opened. The water then flows through the turbines, which turn the generators for producing electricity.
Tidal fences are giant turnstiles that have the potential to cross the straits between an island and the mainland and channels between small islands. The turnstiles can be rotated through tidal currents of coastal waters. These currents run at 5.6 to 9 mph for generating winds of higher velocity. As seawater has high density than air, ocean currents produce more energy than air currents.
Tidal turbines are arranged underwater in rows like wind turbines. These turbines can work best in regions where the coastal currents run between 4 and 5.5 mph. With currents of that speed, a 15-m diameter tidal turbine is capable of producing energy equivalent to that of a 60-m diameter wind turbine. Tidal turbine farms can be located close to shore in water at a depth of 65.5 to 98.5 ft.
Advantages of Tidal Power
The key benefits of tidal power include the following:
- Tides are easily predictable
- Inexpensive to maintain
- Reliable and renewable source of energy
- High energy density than other renewable energy forms
- It produces no greenhouse gases or other waste
- Vertical-axis turbines and offshore turbines are inexpensive to build and have less environmental impact
- Tidal turbines are 80% efficient, which is higher than solar or wind energy generators.
- Barrages reduce the damage of high tidal surges on the land.
Disadvantages of Tidal Power
The following are some of the limitations of tidal power:
- Initial construction cost is very high
- Formation of silt behind the barrage
- Effect on animals and plants living near tidal stations
- Very few suitable sites for constructing barrages
- Disturbs migration of living creatures in the ocean
- Water cannot be replenished, and hence dirt gets settled within the coast
- It produces power for only about 10 h of the day when the tide is moving in and out.
Environmental Aspects of Tidal Power
Several assessments have identified a number of potential environmental impacts of tidal energy development. Some of them are listed below:
- Emission of electromagnetic fields
- Interference with animal migration and movements
- Noise during construction and operation
- Alteration of waves and currents
- Alteration of substrates, sediment transport and deposition
- Change in habitats of benthic organisms
According to researchers, 2013 could experience a big breakthrough in tidal technologies. MeyGen, a tidal technology company, is planning to use tidal technology in the Pentland Firth that can generate up to 40MW of electricity, sufficient for nearly 38,000 homes during its initial phase. Researchers feel that tidal technology development is more reliable than wind and the quality of the power produced by tidal sources is better than other renewable resources. However, the high capital costs associated with the development of tidal technologies are likely to restrict the development of tidal power in the near future.
Tidal Wave Alternative Energy - Run Time - 4:36mins
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